Piezoelectric materials, such as aluminum nitride and zinc oxide, can be formed as layers on a substrate structure. These piezoelectric layers may be incorporated into electronic applications, such as thin film resonator filters. In order for such resonator filters to function properly, the piezoelectric layers must possess a strong C-axis or (001) polycrystalline orientation or texture normal to a substrate plane. From a manufacturing standpoint, it is desirable to form such piezoelectric layers using high deposition rate processes.
Previously, conventional sputtering techniques were used to form piezoelectric layers. According to such techniques, piezoelectric material was typically deposited at a low deposition rate upon a substrate. Conventional sputtering techniques, however, have limited process space, thus resulting in piezoelectric layers having poor (001) polycrystalline texture when deposited at high deposition rates.
More recently, conventional chemical vapor deposition and plasma-assisted ultra high vacuum chemical vapor deposition techniques have been utilized to form piezoelectric layers. Conventional chemical vapor deposition techniques are known to one of ordinary skill in the art. Plasma-assisted ultra high vacuum chemical vapor deposition is a variant of conventional chemical vapor deposition in which deposition occurs at very low pressures. The low deposition pressures promote molecular flow conditions in a reactor so that chemical reactions occur directly on a substrate surface, not in a gas phase. A variety of source material constituents, such as gases or organometallic vapors, can be used in a plasma-assisted ultra high vacuum chemical vapor deposition technique. These source material constituents can be subjected to various processes, such as direct injection, evaporation, and plasma or thermal decomposition or pre-cracking. Like the conventional sputtering techniques, however, the conventional chemical vapor deposition and plasma-assisted ultra high vacuum techniques produced piezoelectric layers with poor (001) texture at high deposition rates.